Some Swans Don't Swim - The Slayer's Reverse Harem, #5.5

Even vampire slayers deserve a holiday.How dare someone knock on the door of Belle Harrison and her super-sexy vampire harem's house. Especially the prickly devil bastard himself. He needs her help to track down an escaped demon who's kidnapping children. If she doesn't, the missing kids won't see their next Christmas. The key to capturing the demon? Seven swans. Soon, it's a race against time to figure out what the hell that means and save the kids.
Or this jolly holiday could be Belle's last.